The present invention concerns an alarm control mechanism including a member that triggers a striking mechanism, a rotating hour cam with a radial recess, a cam follower that abuts approximately radially against the hour cam and whose movement can activate the striking mechanism trigger, and manual means for setting the alarm time, arranged for adjusting the relative angular position of the hour cam and the cam follower.
The term “alarm” designates not only the striking system in alarm timepieces, but any device that generates a signal (also called an alarm) at a pre-selected time in any timepiece, particularly a watch.
CH Patent No. 341771 illustrates an example of a mechanism of this type and it includes a rocking lever, one arm of which is pushed by a spring to follow the edge of a rotating spiral-shaped cam with an abrupt radial recess. The cam is friction mounted, so that its angular position can be adjusted to set the alarm time, on a wheel, which is driven by the timepiece movement and completes one revolution in twenty-four hours. The other arm of the lever cooperates with the means triggering the striking mechanism and with a push-button for stopping the striking mechanism. This type of lever occupies a considerable amount of space beside the cam, which can be a drawback, particularly in a large complication watch.
The usual alarm control mechanisms, for example that described in GB Patent No. 1397982, include two coaxial wheels with a frontal cam system between them, so that, at the alarm time, one of the wheels moves axially towards the other and thus triggers the striking mechanism. The main drawbacks of these mechanisms are their relative lack of precision as to the moment the alarm is triggered, and problems to reset the system, so that it strikes again 24 hours later without having to be specially reset by action by the user.